The invention generally relates to intravascular flow pumps and more particularly pertains to a pump configuration wherein a pumping segment and drive unit are combined along a common axis.
Intravascular flow pumps have previously been described which are introduced into the body by puncturing a vessel in the vascular system and then advanced through such vessel to the site where fluid is to be pumped. The maximum diameter of any components that are introduced into the vessel is limited so as to facilitate their passage through the entire vessel path between the point of entry and the pumping site. Additionally, maximum rigid length must be limited so as to permit the device to be maneuvered around the bends and convolutions that may be encountered along such vessel path. In the case of a blood pump used for left ventricular support for example, such limits have been found to be about 8.0 mm in diameter and 6 cm of rigid length to ensure uninhibited passage up the femoral artery, around the aortic arch and into the heart. In the case of a blood pump used for right ventricular support, such limits have been found to be about 15 mm in diameter and 10 cm of rigid length to insure uninhibited passage up the femoral vein and up through the interior vena cava into the right atrium of the heart. Intravascular pumps may also be placed surgically into the left ventricle either via an aortotomy in retrograde placement across the valve or into the right ventricle via artereotomy in the pulmonary artery and placed retrograde through the pulmonary valve or from the vena cava through the right atrium, right ventricle and pulmonary artery. Such techniques similarly require the rigid length to be minimized so as to facilitate placement. Additionally, it is most desirable to be able to monitor the positioning of the pump relative to the anatomy in order to optimize performance and to prevent injury.
As is described in EP 0 157 871 B1 and EP 0 397 668, intravascular heart pumps are known, in which the pumping segment is driven by a remotely disposed drive unit. The impeller, which is rotatably disposed in a tubular housing, is linked with an extracorporeal drive unit by a flexible shaft or cable which runs through a catheter. The drive unit rotates the flexible shaft which, in turn, drives the pumping segment. Such configuration enjoys certain advantages due to the extracorporeal location of the drive unit in that the drive unit is not subject to a size limitation and therefore does not need to have a high specific power output. Additionally, any heat generated by the drive unit does not impact the patient and because the unit does not contact the patient, it can readily be reused. In an effort to reduce friction between the shaft and the catheter, continuous lubrication is necessary, with the attendant risk that a portion of such lubricant, may pass through the seals of the pump unit and into the blood stream. In addition, the flexible shaft precludes access to those places in the body where excessively sharp bends of the drive shaft would be necessary.
The blood pump described in WO 94/09835 provides for temporary support of the heart. Such blood pump, which is used on the surgically opened heart, has a cylindrical housing which contains the motor and the pump, however, only the pumping segment is positionable within the aorta while the motor portion remains outside the vessel. An intravascular blood pump is described in EP 0 157 859 B1, in which the motor portion and the pump portion are structurally united. Although such device is implantable, it is not however advanceable through the vasculature to the pumping site and its implantation therefore requires a fairly invasive procedure.
More recently, miniaturized drive units and pumping segments have been combined to provide intravascular pumps. However, a number of challenges are inherent in the necessary miniaturization of the components. For example, it is necessary for the drive unit to have an extremely high specific power output yet its surface temperature must never exceed 40.degree. C. in order to avoid denaturization of albumin and/or tissue damage. Moreover, due to the limited amount of power that is available from a miniaturized drive unit and due to the size reduction in the pumping segment that is necessary in order to accommodate the drive unit in the limited amount of space that is available, the pumping segment must be especially efficient, capable of pumping fluids at substantial flow rates for extended periods of time. In the event a relatively fragile fluid such as blood is to be pumped, it is imperative that the required flow rate is achieved without shear and/or cavitation so as to prevent excessive hemolysis. Additionally, flow over the surfaces of the pump must be managed so as to avoid distorted flow pattern or areas of low flow in order to prevent thrombogenisis. Furthermore, in order to maintain optimum performance, it is necessary to stabilize the position of the device to prevent radial, axial and/or rotational movement. It is additionally most desirable to be able to continually monitor the pump's position and performance in order to determine whether any adjustments are necessary.
The presence of the drive unit within the body requires its interior to be properly sealed so as to prevent the transfer of fluids from within the drive unit into the patient or the incursion of fluids from the patient into the drive unit. The former contingency could have a toxic or embolic effect on the patient while the incursion of fluid into the drive unit would result in reduced performance and could damage the internal components. Adequate sealing of the drive unit must however be balanced against any increases in energy demand or by any compromise of its durability and thrombogenicity. Finally, it is most desirable to minimize the costs associated with the use of intravascular flow pumps either by reducing manufacturing costs and/or by maximizing the number of reusable components.
Thus, there is a need for an improved intravascular microaxial pump that is capable of reliably, safely, and efficiently pumping fluids for extended periods of time at high flow rates without cavitation, intolerable shear or heat build-up.